1. Field of the Invention
This invention relates to an electron source and an image forming device, such as a display device, that is an application thereof. More particularly, the invention relates to an image forming device and an image forming method in which a plurality of cold cathode electron sources are arrayed two-dimensionally in a plane to present a color display.
2. Description of the Related Art
Two types of electron sources, namely thermionic cathode and cold cathode electron sources, are known as electron emission devices. Examples of cold cathode electron sources are electron emission devices of the field emission type (abbreviated to "FE" below), metal/insulator/metal type (abbreviated to "MIM" below) and surface-conduction emission type (abbreviated to "SCE".
Known examples of the FE type are described by W. P. Dyke and W. W. Dolan, "Field emission", Advance in Electron Physics, 8.89 (1956) and by C. A. Spindt, "Physical properties of thin-film field emission cathodes with molybdenum cones", J. Appl. Phys., 47.5248 (1976).
A known example of the MIM type is described by C. A. Mead, "The tunnel-emission amplifier", J. Appl. Phys., 32.616 (1961).
A known example of the SCE type is described by M. I. Elinson, Radio. Eng. Electron Phys., 10 (1965).
The SCE type makes use of a phenomenon in which an electron emission is produced in a small-area thin film, which has been formed on a substrate, by passing a current parallel to the film surface.
Various examples of this surface-conduction electron emitting devices have been reported. One relies upon a thin film of SnO.sub.2 according to Elinson, mentioned above. Other examples use a thin film of Au [G. Dillmer: "Thin Solid Films", 9.319 (1972)]; a thin film of In.sub.2 O.sub.3 /SnO.sub.2 [M. Harwell and C. G. Fonstad: "IEEE Trans. E. D. Conf.", 519 (1975)]; and a thin film of carbon [Hisashi Araki, et al: "Vacuum", Vol. 26, No. 1, p. 22 (1983)].
FIG. 33 illustrates the construction of the device according to M. Hartwell, described above. This device is typical of the surface-conduction electron emitting devices. As shown in FIG. 33, numeral 2501 denotes an insulative substrate. Numeral 2502 denotes a H-shaped thin film for forming an electron-emitting region. The thin film 2502 comprises a thin film of a metal oxide formed by sputtering. An electron-emitting region 2503 is formed by an electrification process referred to as "forming", described below. Numeral 2504 designates a thin film, which includes the electron-emitting region 2503 formed on the thin film for forming the electron-emitting region. Further, L1 is set to 0.5.about.1 mm, and W is set to 0.1 mm.
In these conventional surface-conduction electron emitting devices, generally the electron-emitting region 2503 is formed on the thin film 2502, which is for forming the electron-emitting region, by the so-called "forming" electrification process before electron emission is performed. According to the forming process, a voltage is impressed across the thin film 2502, which is for forming the electron-emitting region, thereby locally destroying, deforming or changing the property of the thin film 2502 and forming the electron-emitting region 2503, the electrical resistance of which is high.
The forming process causes a crack in part of the thin film 2502, which is for forming the electron-emitting region. Electrons are emitted from the vicinity of the crack. In the surface-conduction electron emitting devices that has been subjected to the above-described forming treatment, a voltage is applied to the thin film 2502, and a current is passed through the device, whereby electrons are emitted from the electron-emitting region 2503.
Various problems in terms of practical application are encountered in these conventional surface-conduction electron emitting devices. However, the applicant has solved these practical problems by exhaustive research regarding improvements set forth below.
Since the foregoing surface-conduction electron emitting devices is simple in structure and easy to manufacture, an advantage is that a large number of devices can be arrayed over a large surface area. Accordingly, a variety of applications that exploit this feature have been studied. For example, electron beam sources and display devices can be mentioned. As an example of a device in which a number of surface-conduction electron emitting devices are formed in an array, mention can be made of an electron source in which surface-conduction electron emitting devices are arrayed in parallel and both ends of the individual devices are connected by wiring to obtain a row, a number of which are provided in an array (for example, see Japanese Patent Application Laid-Open NO. 1-031332, filed by the applicant).
Further, in an image forming device such as a display device, flat-type displays using liquid crystal have recently become popular as a substitute for CRTs. However, since such displays do not emit their own light, a problem encountered is that they require back-lighting. Thus, there is a need to develop a display device of the type that emits its own light.
Since the foregoing surface-conduction electron emitting devices is structurally simple and readily lends itself to manufacture, an advantage is that a large number of devices can be arrayed over a large surface area. Accordingly, there area a variety of applications that exploit this feature.
Certain problems arise in prototype image forming devices produced using the known surface-conduction electron emitting devices described above. These problems will now be described.
By way of example, a display device shown in FIGS. 34 and 35 has been developed, as described in the specification of Japanese Patent Publication No. 45-31615. FIG. 35 illustrates the display device as seen from the direction of arrow A in FIG. 34. The display device includes serially connected lateral-current electron emission bodies 2512 and stripe-shaped transparent electrode 2514 arranged so as to form a lattice together with the electron emission bodies 2512. Glass plates 2513 each having a small hole 2513' are arranged between the lateral-current electron emission bodies 2512 and the transparent electrode 2514. The glass plates 2513 are arranged in such a manner that the holes 2513' will be situated at positions where they intersect the lateral-current electron emission bodies 2512 and the transparent electrode 2514. Furthermore, a gas is sealed in the holes 2513'. Only the intersection between a lateral-current electron emission body 2512 emitting electrons and a transparent electrode 2514 to which an accelerating voltage E2 is applied emits light owing to electrical discharge of the gas.
Though the lateral-current electron emission body 2512 is not described in detail in the aforesaid specification of Japanese Patent Publication No. 45-31615, the disclosed material (a metallic thin film, a NESA film) and the structure of a neck portion 2512' are identical with those of the surface-conduction electron emitting devices set forth above, and therefore it is believed that the disclosed device falls within the scope of a surface-conduction electron emitting devices. (Furthermore, the term "surface-conduction electron emitting devices" used by the inventors of this application is in line with the description given in thin-film handbooks.)
The problems encountered with the foregoing display device are as follows:
(1) Electrons emitted from the lateral-current electron emission bodies are accelerated and collide with the gas molecules to produce an electric discharge in the display device. However, even if the same current is passed through a lateral-current electron emission body, there is a disparity in the luminance of the light emitted by the discharge and luminance fluctuates even for one and the same pixel. This is caused by the fact that the strength of the discharge is highly dependent upon the state of the gas, thereby resulting in poor controllability. Another cause is that the output of the lateral-current electron emission body is not always stable under a pressure of 15 mmHg, which is of the kind introduced in an experiment. For these reasons the aforesaid display device finds difficulty in presenting a multiple-tone display, and use of such a display device is limited. PA1 (2) Though it is possible to change the color of the emitted light by changing the type of gas sealed in the aforesaid display device, the wavelength of visible light generally obtained with a discharge light emission is limited and a wide range of colors cannot always be displayed. In addition, there are cases in which the optimum pressure of the discharge light emission differs depending upon the type of gas. Accordingly, when it is attempted to change the color displayed by a single panel, it is necessary to change the type and pressure of the gas sealed in each hole. This results in a panel having a very complicated structure. Stacking three panels in each of which a different gas is sealed in order to produce a change in color is unrealistic. PA1 (3) The aforesaid display device has a complicated structure since it is a combination of such components as the substrate of the lateral-current electron emission bodies, the transparent electrodes and gas-filled holes. This makes it difficult to provide an inexpensive display device. Further, as illustrated in the aforementioned patent publication, the threshold voltage of the discharge light emission is a high 35 V. This means that it is necessary to use electrical devices having a high withstand voltage in the electrical circuitry that drives the panel. This also is a cause of an increase in the cost of the display device. PA1 (1) Specifically, there is provided an image forming device having an electron-beam generating source in which a plurality of surface-conduction electron emitting devices are arrayed on a substrate, and phosphors for the three primary colors red, green and yellow for emitting light in response to being irradiated with electron beams from the electron-beam generating source, at least the electron-beam generating source and the phosphors being sealed in an evacuated vessel, and modulating means for modulating the electron beams, which irradiate the phosphors, based upon an image signal, wherein the modulating means has correcting means for subjecting the image signal to a gamma correction. PA1 (2) The electron-beam generating source capable of being used in the color display device of the invention includes a plurality of surface-conduction electron emitting devices arrayed two-dimensionally on the substrate, the devices being connected in the form of a matrix by wiring in a row direction and wiring in a column direction. PA1 (3) In the color display device having the electron-beam generating source mentioned in (2) above, the modulating means has correcting means for correcting the image signal based upon a gamma characteristic, of emission-current intensity vs. applied voltage, of the surface-conduction electron emitting devices. PA1 (4) Further, the modulating means has correcting means for correcting the image signal based upon a gamma characteristic, of light-emission intensity vs. amount of electron beam irradiation, of the phosphors. PA1 (5) The electron-beam generating source capable of being used in the color-image display device of the invention includes a device group in which a plurality of surface-conduction electron emitting devices are arrayed along a row direction on the substrate, and an electrode array in which grid electrodes are arrayed along a column direction, which is substantially perpendicular to the row direction, on or off the substrate. PA1 (6) In the color-image display device having the electron-beam generating source mentioned in (5) above, the modulating means has correcting means for correcting the image signal based upon a gamma characteristic, of light-emission intensity vs. amount of electron beam irradiation, of the phosphors. PA1 (7) The modulating means has correcting means for correcting the image signal based upon a gamma characteristic, of amount of electron beam transmission vs. grid-electrode application signal, of the grid electrodes. PA1 (8) In the color-image display device of the invention, a modulating method for modulating the electron beams that irradiate the phosphors includes modulating length of time (pulses), during which the phosphors are irradiated with the electron beams, based upon the gamma-corrected image signal. PA1 (9) In the color-image display device using the modulating method of (8) above, the modulating means has means for adjusting the modulating signal, which is for modulating the electron beams, independently for each of the color components (red, green, blue). PA1 (10) The means for adjusting the modulating signal, which is for modulating the electron beams, independently for each of the color components (red, green, blue) includes a comparator provided individually for each color component of the gamma-corrected image signal, the adjusting means independently adjusting a correlation between a comparison reference of each comparator and the image signal. PA1 (11) The means for adjusting the modulating signal, which is for modulating the electron beam, independently for each of the color components (red, green, blue) includes an amplifier, the amplification factor of which is capable of being adjusted independently, and a comparator, the amplifier and comparator being provided for each color component of the gamma-corrected image signal, the image signal amplified by the amplifiers being compared with reference values in the comparators, whereby modulated pulses are generated. PA1 (12) The means for adjusting the modulating signal, which is for modulating the electron beams, independently for each of the color components (red, green, blue) includes a pulse-width modulator provided individually for each color component of the gamma-corrected image signal, the adjusting means independently adjusting the frequency of an operating reference clock of each pulse-width modulator. PA1 (13) In the color-image display device of the invention, a modulating method for modulating the electron beams that irradiate the fluorescent bodies includes modulating current amplitude of the electron beams, which irradiate the phosphors, based upon the gamma-corrected image signal. PA1 (14) In the color-image display device using the modulating method of (13) above, the modulating means has means for adjusting the modulating signal, which is for modulating the electron beams, independently for each of the color components (red, green, blue). PA1 (15) The means for adjusting the modulating signal, which is for modulating the electron beams, independently for each of the color components (red, green, blue) includes a level shifter provided individually for each color component of the gamma-corrected image signal, the adjusting means independently adjusting amount of shift of each level shifter. PA1 (16) The means for adjusting the modulating signal, which is for modulating the electron beams, independently for each of the color components (red, green, blue) includes an amplifier provided individually for each color component of the gamma-corrected image signal, the adjusting means independently adjusting the amplification factor of each comparator.
Thus, the problems set forth above arise in a case where light is emitted and color produced by inducing an electrical discharge in gas using the conventional surface-conduction electron emitting devices.
There is a method available which uses phosphors as a structural device for emitting light and producing color in an image display device equipped with surface-conduction electron emitting devices. However, the luminance of the light emitted by phosphors generally has a non-linear characteristic with respect to the density of the current with which it is irradiated. Further, this characteristic is not the same for each of the primary colors [red (R), green (G) and blue (B)]. Accordingly, in a case where the irradiation current value is made the same variable quantity with regard to each of the colors R, G, B, the ratio of the light-emission luminances among the colors R, G, B before and after a change generally differs. In other words, the balance of each color differs.